Characteristics of f-block elements:
(i) The elements in which the last electron enters in f-orbital are called f-block elements.
(ii) This block consists of 4f block elements and 5f block elements.
Lanthanoid series (4f) ₅₈Ce^- ₇₁Lu
Actinoid series (5f) ₉₀Th^- ₁₀₃Lr
(iii) Their general electronic configuration is (n - 2) f^1-14 (n - 1)d^0-1 ns².
Lanthanoid - 4f^1-14 5d^0-1 6s²
Actinoid - 5f^1-14 6d^0-1 7s²

Characteristics of p-block elements:
(i) General electronic configuration is ns²np^1-6 (Group 13 to 18).
(ii) They are generally non-metals but some metals and metalloids are present.

• Non-metallic character increases from left to right along period.
• Metallic character increases on moving down a group.

(iii) They have high electron affinity and ionization enthalpy.

• Both the properties increase along the period.
• Both the properties decrease on moving down the group.

(iv) Oxidising character.

• Increases on moving from left to right along a period.
• Reducing character increases from top to bottom in a group.

(v) s-block and p-block elements are collectively called representative elements.

Elements	Belonging to Groups	Electronic Configuration	Reason for their Name
s-block	1 and 2	ns1 and ns2	Valence electron enters the s-orbital
p-block	13 to 18	ns2np1 to ns2np6	Valence electron enters the p-orbital
d-block	3 to 12	(n-1)d1-10ns(0-2)	Valence electron enters the d-orbital
f-block	lanthanides and Actinoids	(n-2)f1-14(n-1)d0-1ns2	Valence electron enters the f-orbital

Anomalies of Mendeleev's periodic table:
(i) Some elements with similar properties were placed in different groups whereas some elements having dissimilar properties were placed in same group. Eg: Tellurium (127.6) was placed in VI group but iodine (127.0) was placed in VII group.
(ii) Some elements with higher atomic weights were placed before lower atomic masses in order to maintain the similar chemical nature of elements. This concept was called inverted pair of elements concept. Eg: \(_{ 27 }^{ 59 }{ Co }._{ 28 }^{ 58.7 }{ Ni }\) .
(iii) Isotopes did not find any place in Medeleev's periodic table.
(iv) Position of hydrogen could not be made clear.
(v) He did not leave any space for lanthanides and actinides which were discovered later on.
(vi) It could not explain the variable valencies of elements.
(vii) Elements with different nature were placed in one group as 'A' and 'B'; Eg: Alkali metals & coinage metals were placed together.
(viii) Diagonal and horizontal relationships were not explained.

(i) According to the recommendation of IUPAC, the groups are numbered from 1 to 181A.
(ii) There are 18 vertical columns which constitute 18 groups or families.
(iii) There are 7 horizontal rows of the periodic table known as periods.
(iv) The first period contains two elements. One present in first group and the other in 18th group.
(v) Second and third periods contain 8 elements in each.
(vi) Fourth and fifth periods are completely filled as they contain 18 elements in each.
(vii) The sixth period contains 32 elements. The seventh is incomplete. Fourteen elements of both sixth and seventh periods are placed in separate panels at the bottom of the table.
(viii) This periodic table is important and useful because we can predict the properties of any element using periodic trend.